The control and regulation of AC and DC voltages has historically been performed by a variety of techniques. One prior technique particularly well suited to switch an AC or pulsed signal used the saturable reactor. More particularly, saturable reactors have been used to regulate AC and pulsed unipolar input signals.
Although saturable reactors were widely used for many years, the development of high-power semiconductor switches (e.g., the thyristor) reduced the use of saturable reactors. Thereafter, the development of high frequency switching converters in the 1970's lead to a resurrection in the usage of saturable reactors. Particularly, the 1970's development of square cores made of low-loss amorphous alloys contributed to the utility of saturable reactors in high-frequency switching power converters.
Even more recently, improvements have been made in the performance of high-speed solid-state switching devices such as, for example, MOSFETs and IGBTs. Thus, once again, solid-state switches have become an attractive alternative to saturable reactors in high-frequency power converters.
Unfortunately, the use of high-speed solid-state switches in modern power converters requires complex and costly control circuits. These circuits are typically implemented in the form of integrated circuits specifically designed for controlling power converters and are generally known as "synchronous switch controllers" or "secondary-side post-regulator controllers". Pulse with modulation is used in these circuits to control the duty cycle of the solid-state switch. In some examples, these circuits generate the pulse width modulated signal by using a SAW tooth oscillator synchronized to an AC waveform in combination with a comparator and assorted logic.
In view of the above, the simplicity of control associated with the saturable reactor makes it a desirable alternative to high speed switching devices in combination with expensive and complex control circuitry. The traditional, magnetic saturable reactor can be expensive and complex to produce, expensive in terms of real estate within a circuit, and has several non-ideal performance parameters resulting from magnetic core and winding interaction and other transformer-type losses and anomalies.
The present invention is directed towards a solution to the above-identified problems.